There were no working smoke detectors in the New Jersey house where four young kids and their grandmother were killed in a 2,000-degree fire, authorities said yesterday.

The apartment where the victims died had no smoke detectors at all, and those in the adjoining unit weren’t working, said South Plainfield Fire Chief Tom Scalera.

“There were no alarms going off when we arrived,” said Scalera.

The fire started in the kitchen of 1407 Clinton Ave. All five victims were trapped on the second floor. The cause is under investigation.

Gerard Avalos, who owns the 143-year-old house, claimed yesterday that the smoke detectors were working when he inspected them in October.

He added that the family of nine was on Section 8 housing, and that the assistance program inspected the house for safety issues every year.

“I feel very sorry,” Avalos said. “They didn’t have much before, and they have less now.”

Law-enforcement sources told The Post that cops were called several times to escort child welfare workers on visits to the home, where Natalie Jefferson lived with her mother and seven children.

The hellish blaze began at about 3 a.m. Thursday and quickly consumed the converted farmhouse. Grandmother Ann Jefferson, 62, was killed, along with grandchildren Alize, 12; Tyler, 7; Christopher, 3; and Elijah, 2.

Their brother Jordan, 8, is bandaged from the neck down at a nearby burn center, according to his family.